Process for the production of glycolic acid

Abstract

A process for the production of glycolic acid or a derivative thereof comprises: reacting formaldehyde with carbon monoxide and water in a carbonylation reactor in the presence of a sulfurcatalyst, said reactor operating under suitable conditions, such that glycolic acid is formed; recovering a first product stream comprising glycolic acid, impurities and a sulfur species in the carbonylation reactor; passing the first product stream to an esterification reactor where it is subjected to esterification to form an alkylglycolate and wherein the esterification is catalysed by the sulfur species recovered in the first product stream; recovering a second product stream comprising the alkylglycolate, sulfur species and impurities from the esterification reactor; separating the sulfur species from the second product stream and recycling it to the carbonylation reactor in step (a) to form a sulphur depleted second product stream; separating the alkylglycolate from the sulphur depleted second product stream in a distillation zone; and recovering the alkylglycolate and converting the alkylglycolate to glycolic acid.

Claims

1. A process for the production of glycolic acid or a derivative thereof comprising: (a) reacting formaldehyde with carbon monoxide and water in a carbonylation reactor in the presence of a sulfur catalyst to form glycolic acid; (b) recovering a first product stream comprising glycolic acid, impurities, and a sulfur species in the carbonylation reactor; (c) passing the first product stream to an esterification reactor where it is subjected to esterification to form an alkylglycolate and wherein the esterification is catalysed by the sulfur species recovered in the first product stream; (d) recovering a second product stream comprising the alkylglycolate, sulfur species, and impurities from the esterification reactor; (e) separating the sulfur species from the second product stream and recycling it to the carbonylation reactor to form a sulphur depleted second product stream; (f) separating the alkylglycolate from the sulphur depleted second product stream in a distillation zone; and (g) recovering the alkylglycolate and converting the alkylglycolate to glycolic acid.

2. The process according to claim 1, wherein the alkylglycolate is converted to glycolic acid in an hydrolysis reactor.

3. The process according to claim 1, wherein the molar ratio of water:formaldehyde is about 4:1.

4. The process according to claim 1, wherein a solvent is used in the carbonylation reactor.

5. The process according to claim 4, wherein the solvent is propionic acid or a sulphone.

6. The process according to claim 5, wherein the solvent is 2,3,4,5-tetrahydrothiophene-1,1-dioxide.

7. The process according to claim 1, wherein the carbonylation reactor is operated at a temperature in the range of from about 50 C. to about 400 C., and at a pressure in the range of from about 1 to about 1000 bara (about 0.1 to about 100 MPa).

8. The process according to any one of claim 1, wherein the first product stream is passed to a lights separation zone.

9. The process according to claim 8, wherein the light separation zone is operated at a reboiler temperature of about 140 C. to about 160 C., an overhead temperature of about 75 C. to about 85 C., and a pressure of about 1.8 bara to about 2.2 bara.

10. The process according to claim 8, wherein a low boiling point alkanol is supplied to the lights separation zone.

11. The process according to claim 8, wherein an overhead recovered from the lights separation zone is passed to a water separation zone.

12. The process according to claim 11, wherein an overhead from the water separation zone is fed to a formaldehyde separation column.

13. The process according to claim 1, wherein the esterification is carried out at a temperature of from about 90 C. to about 150 C.

14. The process according to claim 1, wherein the esterification reactor is operated at a pressure of from about 3 bara to about 7 bara.

15. The process according to claim 1, wherein the sulfur species is removed prior to the sulfur species depleted second product stream being treated to recover the alkyl glycolate.

16. The process according to claim 1, wherein the sulfur species is separated in an esterification flash drum and recovered in a sulfur species stream.

17. The process according to claim 16, wherein the esterification flash drum is operated at a temperature of from about 140 C. to about 160 C., and at a pressure of about 1.5 to about 2.0 bara.

18. The process according to claim 16, wherein the sulfur species is recycled to the carbonylation reactor.

19. The process according to claim 16, wherein the sulfur species stream is passed to a recycle column.

20. The process according to claim 19, wherein water is added to the bottom of the recycle column.

21. The process according to claim 1, wherein the second product stream, or a sulfur-depleted second product stream, is passed to an ester distillation column.

22. The process according to claim 21, wherein the ester distillation column is carried out at a pressure of about 0.2 bara to about 0.4 bara.

23. The process according to claim 21, wherein an overhead temperature in the ester distillation column is about 60 C. to about 65 C., and a bottom temperature is about 130 C. to about 140 C.

24. The process according to claim 1, wherein the alkylglycolate is converted to glycolic acid in a hydrolysis reactor.

25. The process according to claim 24, wherein the hydrolysis reactor is a reactive distillation column.

26. The process according to claim 24, wherein a catalyst is added to the reactive distillation column.

27. The process according to claim 1, wherein the alkylglycolate is converted to glycolic acid by ion exchange.

Description

(1) The present invention will now be described by way of example with reference to the accompanying drawing, in which:

(2) FIG. 1 is a schematic illustration of the process of the present invention; and

(3) FIG. 2 is a schematic illustration of an alternative arrangement of the present invention.

(4) It will be understood by those skilled in the art that the figures are diagrammatic and that further items of equipment such as feedstock drums, pumps, vacuum pumps, compressors, gas recycling compressors, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks and the like may be required in a commercial plant. Provision of such ancillary equipment forms no part of the present invention and is in accordance with conventional chemical engineering practice.

(5) The present invention will be described with particular reference to the formation of a methyl glycolate. However, it will be understood that other alkyl esters may be used.

(6) As illustrated in FIG. 1, formaldehyde, such as 55 wt % aqueous formaldehyde, is passed in line 1 to a mixing tank 2 where it is mixed with the sulfur catalyst added in line 3. The mixed formaldehyde is passed in line 4 to the carbonylation reactor 5 where it is reacted with carbon monoxide which is supplied to the reactor in line 6.

(7) The first product stream is recovered in line 7. This stream will comprise glycolic acid, sulfur species and impurities which may be selected from methyl formate, formic acid, methylal, methanol and formaldehyde. It is passed to a lights separation zone 8 where lights which may include methyl formate, methylal, methanol and formaldehyde will be removed in line 9. Methanol may be added in line 10 to facilitate separation.

(8) A stream including the glycolic acid is taken at or near the bottom in line 11. This will generally be removed below the position of the methanol feed. The stream is then passed to the esterification reactor 12 where it is contacted with methanol added in line 13. The esterification reactor may be a plug flow reactor. A second product stream comprising the methyl glycolate, the sulfur species and impurities is recovered from the reactor in line 14 and passed to the esterification flash drum 15 where the sulfur species are separated.

(9) The sulfur species is recovered in line 16. The pump 17 facilitates the return of the sulfur species and any heavy recycle may be returned to the carbonylation reactor 5. The heavy recycle may be fed directly to the reactor or it may be fed into line 4.

(10) The methyl glycolate is recovered in second product stream in line 18. This stream will also include water, and impurities. This stream is fed to the ester separation column 19 where light impurities such as water, methanol and light by-products are removed as column overheads 20 and heavy impurities such as dimethyl diglycolate are recovered in line 21.

(11) The methyl glycolate may be recovered as a side draw in line 22. This will generally be taken below the point at which feed is added. Where the desired product is glycolic acid, the recovered methyl glycolate may be passed to hydrolysis reactor 23. Methyl glycolate may optionally be taken as an off-take in line 24. Water is supplied to the hydrolysis reactor 23 in line 25. It may also be necessary to add catalyst to the hydrolysis reactor 23. Where this is a heterogeneous catalyst it will be provided on trays within the reactor 23. Where it is a homogeneous catalyst it may be added into line 22 before the methyl glycolate is supplied to the hydrolysis reactor. The glycolic acid is removed from the hydrolysis reactor 23 in line 26 where it may optionally be passed through an ion exchange purifier 27 before being recovered in line 28. Methanol and water is recovered from the hydrolysis reactor as an overhead in line 29. In one alternative, the hydrolysis reactor is replaced with an ion exchange system.

(12) An alternative arrangement is illustrated in FIG. 2. Much of this arrangement is the same as in FIG. 1. In this arrangement, the stream recovered from the bottom of the esterification flash drum 15 is passed in line 30 to a recycle column 31. Water may be added to the recycle column in line 38. The bottom stream from the recycle column 31 is fed in line 16 to the carbonylation reactor 5.

(13) The overheads from the recycle column 31 are passed in line 32 to the water separation column 33. The overhead stream 9 from the lights separation zone 8 may also be passed to the water separation column 33. It may be supplied separately or may be combined with stream 32 before being passed to the water separation column 33. Water is removed from the bottom of the water separation column in line 34.

(14) The overheads from the water separation column are passed in line 35 to the formaldehyde separation column 36. Methanol is recovered in line 38. The overhead will generally be recovered in line 37 and sent to the formaldehyde plant

(15) The present invention will now be described with reference to the following example.

EXAMPLE 1

(16) The simulation platform Aspen Plus V8.8 was used to simulate the esterification and hydrolysis columns. The physical properties used in the simulation were sourced using a combination of Aspen plus databanks, and property estimation methods

(17) The process conditions for the ester separation and hydrolysis columns which are reactive distillation columns, used the following conditions:

(18) TABLE-US-00001 Ester Separation Hydrolysis Column Column Column Top P 0.3 1.2 (bara) Column Top T 61.9 79.2 ( C.) Column Base 133.8 134.0 T ( C.)

(19) The reactions included in the simulation are primarily esterification of glycolic acid (GA), methoxyacetic acid (MAA), diglycolic acid (DGA) with methanol, plus hydrolysis of the resulting esters, namely methyl glycolate (MG), methylmethoxyacetate (MMA), methyl diglycolate (M-DG) and dimethyl digylcolate (M-DG-M). The esterification reaction was catalysed by H.sub.2SO.sub.4.

(20) The stream compositions derived in the simulation are set out in the Table below. The stream numbers correspond to the streams indicated in FIG. 1.

(21) TABLE-US-00002 Composition wt % Catalyst Supplied to line 18 20 21 22 22 25 29 26 28 Lights 0.271 0.492 0 0 0 0 0 0 0 Water 25.415 46.626 0 0 7.0 100.0 15.508 25.005 25.161 GA 0.926 0 13.25 0.507 0 0 0 73.999 74.46 MeOH 25.056 46.013 0 0 0 0 84.387 0.007 0.007 DGA 0 0 0 0 0 0 0 0.208 0.21 MG 43.921 0.1 76.852 99.077 0 0 0.104 0.052 0.052 MAA 0.165 0 2.276 0.095 0 0 0 0.109 0.11 MMA 3.703 6.77 0.001 0.034 0 0 0.001 0 0 M-DG 0.006 0 0.083 0.003 0 0 0 0 0 M-DG-M 0.535 0 7.509 0.283 0 0 0 0 0 Sulphuric acid 0.002 0 0.028 0.001 93.0 0 0 0.618 0 Mass Flow 6501 3542 365 2594 20 1419 1086 2947 2928 (kg/hr)

(22) The lights constitute of formaldehyde, formic acid, methyl formate and methylal.

(23) In the example presented here, the rate of methyl glycolate hydrolysis is enhanced by the addition of a homogeneous catalyst (H.sub.2SO.sub.4) in the feed to the hydrolysis reactor. This could also be achieved via heterogeneous catalysis and/or by operating the column at a higher pressure.

(24) It will be understood that catalyst is required in a number of parts in the flowsheet. Where a homogeneous catalyst, such as sulphuric acid, is used, the catalyst will pass through the flowsheet and so the same catalyst can be used. However, a separate catalyst will generally be required for the final hydrolysis of the product.